The present invention relates to an ophthalmic lens comprising a main lens part and a recessed part.
One particular type of ophthalmic lenses of that type is an Multifocal Intra Ocular Lens (MIOL). It usually comprises a lens part with a centre, which lens part is provided on the periphery with supporting parts (haptics). Lenses of this type are generally known in the state of the art. These are used for replacement of the eye lens after cataract operations, for example many attempts are made to provide MIOL with concentric annular optical zones for reading distance and or intermediate vision. In a “simultaneous vision multifocal”, the relationship between the distance zone and the near zone is quite critical. In order for that type of lens to function properly, it must permit approximately equal amounts of light into the eye through both the near zone and the distance zone. This is required so that vision is not biased toward either vision correction. Obviously, because of the great variation in light levels in daily life, which accordingly change the diameter of the pupil, a compromise must be reached upon when selecting the size of each zone. This problem, also refers to as “pupil dependency”, is further complicated as the difference in pupil size varies substantially from patient to patient. Examples of these types of lenses may be seen in U.S. Pat. Nos. 4,636,049; 4,418,991; 4,210,391; 4,162,172; and 3,726,587, and in patent application US 2006/0212117, EP0590025B1, U.S. Pat. No. 6,126,286. Another problem of those annular concentric designed MIOL are the ghost images and blur due to the light directed to the macula at the annular zone transitions. Another big drawback of current MIOL is the loss of contrast sensitivity. Contrast sensitivity determines the lowest contrast level which can be detected by a patient for a given size target. Normally a range of target sizes are used. In this way contrast sensitivity is unlike acuity. Contrast sensitivity measures two variables, size and contrast, while acuity measures only size. Contrast sensitivity is very similar to auditory testing, which determines a patient's ability to detect the lowest level of loudness of various sound frequencies. The patient is asked to depress a button when the tone is just barely audible and release the button when the tone can no longer be heard. This procedure is used to test auditory sensitivity to a range of sound frequencies. If auditory testing were evaluated in a similar way to visual acuity, all the sound frequencies would be tested at one high level of loudness.
The problem of pupil dependency of simultaneous vision multifocal performance is claimed to be diminished by a further embodiment of simultaneous vision multifocals that operates under the principles of diffraction. Examples of these types of lenses were presented in U.S. Pat. Nos. 4,641,934 and 4,642,112. Due to the nature of diffractive optics, at least 20% of the incoming light will be lost and patients suffer from halos and glare.
To solve this pupil independency several attempts have been made, such as disclosed in U.S. Pat. No. 4,923,296 which describes a lens divided into a series of substantially discrete near and distant vision zones. Not clear from this disclosure is how these vision zones could be made and or joined together. WO 92/06400 describes a aspheric ophthalmic lens. The surface zones are defined three dimensionally forming a junctionless, continuous and smooth surface in conjunction with one another. It will be clear to a person skilled in the art that such a lens will suffer a large decrease of optical quality. U.S. Pat. No. 4,921,496 describes a rotation symmetric, radially segmented IOL. That IOL has no junctions at the surface, since the materials for each segment should have different refractive indices to create the different powers.
Another lens with a distance part and a near part is described in EP0858613(B1) and U.S. Pat. No. 6,409,339(B1) by Procornea Holding B.V. from the current inventor, and which are incorporated by reference as if fully set forth. These documents disclose contact lenses, but also refer to IOL's. A lens of this type differs from other lenses in that the reading part is located within the (imaginary) boundary of the distance part. That is to say the reading part is on or within the imaginary radius of the outer boundary of the distance part (Rv). If a reading part is used this is preferably made as a sector which extends from the centre of the lens. This lens proved to have many possibilities. There is, however, room for further improvement.
It has been found after extensive clinical testing that for a MIOL as disclosed in U.S. Pat. No. 6,409,339(B1), the transition profile used to bridge the step height between the sector boundaries is not optimal. This results in reduction of the usable optical area and significant loss of light energy and contrast sensitivity. The optical configuration as disclosed herein provides a distinct bifocal image whereas a multifocal image is necessary to reduce halo's with big pupil size and at the same time have a clear vision with high contrast at near and intermediate distance. EP0858613(B1) and U.S. Pat. No. 6,409,339(B1) in particular discloses that the transitions should be smooth and have a sigmoid or sine shape curve to bridge the step height difference between both optical parts. U.S. Pat. No. 6,871,953, to Mandell, published September 2003, surprisingly discloses the same use of sigmoid curve types to bridge the step height resulting in exactly the same lens configuration as described in EP0858613 (B1). The purpose of the sigmoid curves in both applications when relating to contact lenses is to make the transitions between the optical parts as smooth as possible to reduce friction of the eyelid. A drawback of the wide transitions described therein is that it also creates a high loss of light energy and was found to reduce contrast sensitivity. U.S. Pat. No. 6,871,953 discloses to make the transitions wider to create even smoother transitions. Due to the alternating principle of a contact lens, the contact lens nowadays moves up on the eye when line of sight is down gaze. The loss of light at the transitions under these alternating conditions for contact lenses is not determined. The opposite, however, is true for a MIOL. Such a lens is fixed in the eye. The optical usable area of the semi-meridian sectors will be reduced, which leads to less light energy being directed to the macula. This results in poor optical performance either for distance or near vision. Furthermore it has been found that due to the fact that the pupil size varies under different light conditions, unwanted halo effects may occur with big pupil size. Therefore it would be beneficial to have a apodized power profile in the reading part to reduce this phenomenon and introduce multifocallity at same moment.
U.S. Pat. No. 7,004,585 discloses a multifocal contact lens having a blended design for a segmented optical zone. The contact lens should move on the eye easily in order to make the lower reading zone available. Furthermore, a transition or blend zone should be designed to avoid blur and ghost images. To that end, the blend zone should have a smooth transition to improve wearers comfort. Furthermore, the blend zone should include a curvature magnitude to refract light away from the macular region of the eye. The various optical zones should influence each other as little as possible. In this document, patentee seems to have identified that problem. The solution of making the blend zone as smooth as possible and providing a reading zone in a particular way, however, seems complex. The ophthalmic lens design can be further improved, however. In particular for IOL devices, there is room for further improvement.
In U.S. Pat. No. 7,237,894, a ophthalmic lens was designed with a radial centre below the centre of the optical zone. In that way, however, it is difficult to avoid an image shift.